Molecular Analysis of Flagellar Hook Genes in the Oral Spirochete, Treponema denticola Oral spirochetes are prominent members of microbial flora in periodontal disease sites and are capable of penetrating host tissues. Spirochetal motility, which can be considered a virulence factor, is attributable to flagella which structurally resemble flagella from other microorganisms. Spirochetes are unique, however, in that the flagella are confined to the periplasm, arising from both poles of the cell. The mechanics and regulation of flagellar assembly and directed movement in spirochetes are issues which remain largely unexplored. A clone, derived irom the periodontal spirochete, Treponema denticola and selected on the basis of immunoreactivity during screening of a genetic library with sera from patients with adult periodontitis, was found to contain the flagellar switch and basal body genes, fliG, and fliF. Analysis of the region 5' to fliF revealed the presence of three contiguously arranged genes whose predicted products appear to be homologs of the flagellar hook basal body proteins, FlgB, FlgC and FliE. Efforts are currently underway to explore the regulation and transcriptional orgniation of these genes in T. denticola. Information obtained from this clone may elucidate how spirochetes synthesize and assemble flagellar components and the relevance of antiflagellar antibodies in periodontal disease.